Photoresponsive Gels Prepared by Ring-Opening Metathesis Polymerization

This communication describes photoresponsive gels, prepared using ring‐opening metathesis polymerization (ROMP), that dissolve upon irradiation with ultraviolet light. Exposure of mixtures of norbornene‐type ROMP monomers and new photoreactive cross‐linkers comprising two norbornene units bound through a chain containing o‐nitrobenzyl esters (NBEs) to well‐known ruthenium carbene catalysts gave cross‐linked polymer networks that swelled in organic solvents or water depending on the structure of the monomer. These gels became homogeneous upon irradiation with UV light, consistent with breaking of the cross‐links through photolysis of the NBE groups. The irradiation time required for homogenization of the gels depended on the cross‐link density and the structure of the photoresponsive cross‐linker. Light‐responsive gels combine ring‐opening metathesis polymerization (ROMP) with novel photoresponsive bis(norbornene) cross‐linkers containing photolabile nitrobenzyl esters. Upon addition of commercially available ruthenium carbene catalysts, gelation is complete in a matter of minutes. Irradiation with UV light causes ROMP‐derived organogels or hydrogels to swell and dissolve due to photolysis of the nitrobenzyl groups in the cross‐linkers.